All electrochemical cells or batteries contain a negative terminal (an anode) and a positive terminal (a cathode) that are separated from each other by an electrolyte. When a battery is connected to an external circuit, the electrolyte is able to move as ions within the battery, and chemical reactions occur at each terminal that deliver energy to the external circuit.
Physical separation of the positive terminal from the negative terminal is maintained by a permeable membrane or separator. Historically, separators have been fabricated from non-woven materials such as paper, porous rubber, celluloid, or cellophane. More recently, separators have been fabricated from some non-woven non-cellulosic polymers, including polyamides, polyvinyl alcohol (PVOH), polyesters, and polypropylenes.